Danny Espinosa's RBI single in the top of the 12th inning and a game-saving grab by Roger Bernadina in the bottom half was the difference as Washington claimed a 3-2 win over Houston in the second edition of a four-game set.
Espinosa drove in Michael Morse -- who extended his hit streak to a career- best 16 games -- to give the visitors the lead, then Bernadina crashed into the padding along the wall in left center to rob Brett Wallace of a potential game-winning extra-base hit.
"It was sensational." Nationals manager Davey Johnson said about Bernadina's catch. "He disappeared and then he came out holding the glove high and I said 'This is great. Let's get out of here.'"
That catch made a winner of Drew Storen (1-0) who recorded the final two outs in the 11th, and assured Tyler Clippard of his 23rd save.
Espinosa added a two-run homer for the Nationals, who have won the first two in the series and six of seven overall.
Ben Francisco slugged a two-run homer for the Astros, losers in nine of their last 11.
"Honestly I don't think that we can worry about that," said Wallace. "You can't look at those numbers and you can't worry about what has happened in the past. We just have to keep going."
Mickey Storey (0-1) was charged with the deciding run over two relief innings.
Morse began the 12th with a double, then was moved to third on a Bernadina sacrifice bunt and scored on Espinosa's base hit to deep short.
Clippard served up a leadoff infield hit to Steve Pearce then walked Carlos Corporan with two outs. Wallace then stroked a line drive to the gap which was likely to score both runners, but Bernadina saved the day for the NL East leaders.
Francisco's two-run shot in the bottom of the first staked the home team to the lead, then Espinosa countered in the second for the visitors.
Washington's Ross Detwiler departed after seven innings, allowing three hits and two runs. His counterpart, Jordan Lyles, worked seven-plus frames and also gave up three hits and a pair of runs.
Houston failed to score despite two on in the bottom of the ninth.
Washington improved to 10-6 in extra innings this season, while Houston fell to 0-11...Nats outfielder Jayson Werth singled in his lone at-bat, and has reached base in each of his last 18 games dating back to April...Prior to the game, the Astros placed outfielder Jordan Schafer on the 15-day disabled list, recalled outfielder Brandon Barnes from Triple-A Oklahoma City and designated pitcher Juan Abreu for assignment.